NMEA Over UDP

Technical & Application Notes

This feature is available on the VersaSync and SecureSync 2400 products and is used for special applications that require a once-per-second NMEA UDP message to be sent out by the system via multicast. This message will be transmitted within 200 ms of the corresponding rising edge of the 1PPS pulse. NMEA over UDP is configured using CLI commands; there is currently no Web UI page for this functionality.

The NMEA message consists of 3 parts:

  1. A header: Header of the frame
  2. The ZDA data: ZDA NMEA standard message
  3. The SFT data: A proprietary NMEA message that carries system status information
 NameValueType or FormatMinMaxSizeDescription
HEADERSOURCE PORT â€“1024491512Time server port
DESTINATION PORT â€“1024491512Port to be used to send the frame over UDP defined by the user
LENGTH â€“  2Size of the message including the header size
CHECKSUM0x00–  2Fixed value (not used)
MESSAGE ID23Integer––2Fixed value
ZDA DATASTART DELIMITER$ASCII character  1Fixed value
CONSTELLATION SOURCEGPASCII character  2Fixed value
MESSAGE NAMEZDA,ASCII character  4Fixed value
UTC TIME hhmmss.ss,0235959.991 or 10Time of the corresponding 1PPS signal, hence the decimals are always zero
UTC DAY xx,01311 or 3 
UTC MONTH xx,01121 or 3 
UTC YEAR xxxx,099991 or 5 
LOCAL ZONE HOUR [-}xx,-13131, 3 or 4 
LOCAL ZONE MINUTES [-]xx-59590, 2 OR 3 
CHECKSUM *HH  3The checksum at the end of each sentenc is the XOR of all of the bytes in the sentence, excluding the inital dollar sign and * character (in hexa)
END DELIMITER<CR><LF>ASCII character– 2Fixed value
SFT DATASTART DELIMITER$ASCII character– 2Fixed Value
CONSTELLATION SOURCEGPASCII character  2Fixed value
MESSAGE NAMESFT,ASCII character  4Fixed value
TFOM sssssssss,09999999991 or 101 sigma, Positive value, Absolute value of the Estimated Time Error in nanoseconds. TFOM field remains empty when the value is invalid.
POWER STATUS1, 1111: powerd
Fixed value
GNSS STATUS x,0410: No GNSS réception, 0 satellites
1: GNSS is available as reference (1PPS and Time
OK)
2: Antenna short circuit
3: Jamming detected
4: GNSS acquisition in process (≥ 1 satellite(s)), or 1PPS OK, or Time OK)
INPUT STATUS x,0210: Inputs not detected / all input are disabled
1: Inputs are enabled
2: 1 or more input is invalid timing on 1 or more input detected
SYNCHRONIZATION STATUS X,0210: Unit is in Holdover (valid)
1: System clock OK (Valid)
2: Invalid Time (Holdover period exceeded, or oscillator damage)
OUTPUT STATUS X,0210: No output signal(s) detected/all outputs are
disabled
1: Outputs are enabled 1.3 Status LEDs
2: Malfunction detected (short circuit, or
overload)
NETWORK STATUS x,0210: No network detected)
1: Network OK, configuration OK
2: Network malfunction detected (e.g., no auto-
negotiation)
FAULT STATUS x,0410: Unit OK
2: Unit requires attention; check other status LEDs, see Web UI
4: Acquiring fix or SW upgrade
TEMPERATURE STATUS x,0210: Temperature OK
2: High temperature detected
CHECKSUM *he  3The checksum at the end of each sentence is the XOR of all of the bytes in the sentence, excluding the initial dollar sign and * character (in hexa)
END DELIMITER<CR><LF>ASCII character  2Fixed value

System Time Message Service

This service is a proprietary Orolia (formerly Spectracom) daemon which is present on our products. It allows the unit to send a defined message over UDP before every 1PPS signal. The NMEA over UDP feature uses this service to transmit the message described above.

Note: By default, the Safran message is sent over UDP before every 1PPS signal. It contains the time when the next 1PPS discrete will occur. The message format is:

messaging format parameters and description

Configuration of NMEA over UDP

The user can configure the feature by using a command line interface as described below. This configuration is saved in a file (stmd.conf) which is used to replay the configuration after a reboot.

Command Line Interface

The CLI command sendnmeaudp is used to configure, enable, and disable the NMEA over UDP feature. The usage of the command is:

sendnmeaudp <nmea enable> [<multicast address> <port number> <local enable>] [<local hour> <local minute>]

Note: To stop sending an NMEA frame over UDP

Execute: sendnmeaudp 0

Note: To send an NMEA frame over UDP without a local clock

Execute: sendnmeaudp 1 <multicast address> <port number> 0

Note: To send an NMEA frame over UDP with a local clock

Execute: sendnmeaudp 1 <multicast address> <port number> 1 <local hour> <local minute>

Error Messages

The CLI returns error messages when a bad parameter is passed through the command, as follows:

Support

If you have any questions or comments regarding any of the above-mentioned information or instructions, or require assistance, please contact Safran Support Services.

Support Page